The present invention relates to a diode circuit and more particularly to a diode circuit for clamping the signals on the transmission line to the predetermined potential.
A diode circuit of this type consisted of one diode and used to reduce an AC noise in a signal on transmission line by clamping to a particular potential. This diode circuit consisted of one diode was provided with transmission line to transmit the 1.5 V signal from the region having the 1.5 V power supply layer to the region having the 3.3 V power supply layer adjacently located on the region having the 1.5 V power supply layer (hereinafter referred to as related art 1).
Moreover, a diode circuit comprising a plurality of diodes is described in the Japanese Patent Application Laid-Open No. Sho 125958/1979. This diode circuit comprising a plurality of diodes connected in series between the collector of transistor connected to a gate transistor and the ground in order to reduce and fix an output level of the TTL circuit (hereinafter referred to as related art 2).
However, the related art 1 has a problem that when it is required to supply the 1.5 V signal to the area isolated far from the region having the 1.5 V power supply layer among the region having the 3.3 V power supply layer, the effect of clamping is lost and the signal on the transmission line vibrates, because the transmission line becomes long and thereby an inductance element of this transmission line becomes large. Moreover, when the signal on the transmission line has a frequency element as high as 1 GHz, here rises also a problem that the diode circuit of the related art 1 comprising only one diode cannot eliminate such high frequency element. Moreover, the related art 1 also has a problem that clamping at the predetermined potential is impossible because the clamping voltage cannot be set to the voltage lower than 3.3 V even if the signal is clamped with only one diode by using the adjacent 3.3 V power supply layer.
Moreover, the related art 2 is composed of a plurality of diodes only to fix the DC potential in the device and is not intended to eliminate the AC noise element at all. This AC noise element impedes the correct operation in such circuit using a small amplitude signal at a high speed as a GTL (Gunning Transceiver Logic).
It is therefore an object of the present invention to provide a diode circuit which can eliminate high frequency AC noise included in the voltage waveform on the transmission line. Moreover, it is also an object of the present invention to provide a diode circuit which can obtain the desired potential and more particularly to provide a diode circuit capable of obtaining the 1.5 V signal from the region having the 3.3 V power supply layer in the region having the same 3.3 V power supply layer.